Blasting cap and method of making same



NOV. 30, 1954 T. J. MuLQUf-:ENY

BLASTING CAP AND METHOD OF MAKING SAME Filed Aug. 14, 195o /l f M o 9. 5

F IG.

INVENToR. THOMAS J. Mu QUEE Y ATTORNEYS.

United States Patent Utilice 2,695,562 Patented Nov. 30, 1954 BLASTING CAP AND METHOD F MAKING SAME Thomas J. Mulqueeny, Godfrey, Ill., assignor to Olin Mathieson Chemical Corporation, a corporation of Virginia Application August 14, 1950, Serial No. 179,347

2 Claims. (Cl. 102-28) This invention relates generally to blasting caps, and particularly to a closure seal for the end of an electric blasting cap.

In electric blasting caps where a pair of electrical conductors must extend from an ignition assembly to the exterior, an adequate seal must be provided at the open end of the usual shell which contains the explosive charge, so as to waterproof the cap and provide a rm support for the ignition assembly. The presence of the electrical conductors complicates the problem, and the art has long been plagued by the expensive and tedious procedures involved in providing an adequate seal.

The object of the present invention is to provide a seal for electric blasting caps which may be manufactured with facility, and without likelihood that the ignition assembly may be distorted or damaged during the assembly.

Other objects will become apparent to those skilled in the art when the following description is read in connection with the accompanying drawings, in which:

IFigure l is a longitudinal sectional view of a partially assembled electric blasting cap constructed in accordance with the present invention;

Figure 2 is a longitudinal sectional View of the blasting cap shown in Figure l, when the assembly is complete;

Figure 3 is a longitudinal sectional view of another embodiment of the invention; and

Figures 4, 5 and 6 are, respectively, perspective views of the several components of the seal for the electric blasting cap shown in Figures l, 2 and 3.

-In accordance with the present invention, the end closure and seal of an electric blasting cap is formed by compressing a gasket of soft, resilient material between two hard bodies, one of Which constitutes a plug in which the conductors (extending to the ignition assembly) -are embedded, and the said two hard bodies are anchored against relative movement which would release the compression upon the gasket. the gasket is preferably accomplished in situ Within the case of the blasting cap by moving the two hard members relative to each other after they have been assembled with the gasket between them, and then anchoring the two hard members together, so that the gasket is maintained in a compresesd condition, tending to urge the two hard members apart and urging itself into sealing engagement with the interior of the case. One of the hard members is preferably irst positioned in the case, so that it cannot move therein in a direction away from the mouth of the case. The gasket is inserted above said hard member, and iinally, the second hard member is applied on top of the gasket and forceably moved toward the xed first-mentioned hard member to compress the gasket, whereupon the mouth of the case may be nturned to retain the second-mentioned hard member in its lnal position.

Referring now to Figure l of the drawings for an illustrative embodiment of the invention, the usual case 1 is provided with a base charge 2 and an initiating charge 3 seated in the closed end of the case, in accordance with the usual practice. Above the explosive charge a supporting member 4 is provided. As shown, the supporting member 4 is in the form of a cup, having a perforation 5 in the -center thereof. The cup may be formed of metal, or of relatively stiff fibrous material such as paperboard, it being important that the compressive strength thereof axially of the case 1 substantially exceeds the .compressive strength of the gasket hereinafter described.

Seated upon the cup 4 is a molded plug having a body The compression of d portion 6 whose outside dimension corresponds substantially with the inside dimension of the cup 1, so that it may be freely inserted into the cup 1. The plug is formed with a stem portion 7 extending axially from the body 6, and of considerably lesser diameter than the inside diameter of the cup 1. Conductors 8 extend through the plug and project from the interior of body portion 6, where they are provided with a bridge wire 9, or other suitable ignition assembly.

The plug is preferably molded of a suitable thermosetting or thermoplastic molding composition, and the conductors 8 are embedded therein during the process of molding thereby forming a seal at the interfaces between the plug material and the conductors. Preferably the plug is of dielectric material, which is impervious to water.

About the stem 7 a gasket 10 is provided. The gasket has a central opening of a size such as to be freely received over the stem 7, and has an exterior dimension such that it will be freely received within cup 1. The gasket may be formed of rubber, or rubber-like material, which is soft, non-porous and resilient.

Above the gasket 10 is a Washer 11 which, like the plug above-described, may be molded from any suitable thermoplastic or thermosetting composition, or may be of metal, it being important only that the washer be substantially harder than the gasket 10, so that the washer will not deform when subjected to substantial compression.

When the several parts are inserted into the cup 1 as above-described, the washer 11 projects for a substantial extent above the mouth of cup 1. An endwise force exerted upon the washer 1l moves the latter in an axial direction relative to head 6 of the plug, and compresses the gasket 10 therebetween. The endwise force is continued until the washer 11 is positioned below the open mouth of the cup 1. When the washer is thus positioned, the edges of the cup 1 about its mouth are nturned as shown at 12 in Figure 2, in order to anchor the parts against relative movement and to maintain the gasket 10 compressed between head 6 and washer 11. In the process of compression, it will be noted by comparison of Figures l and 2 that the axial dimension of the gasket 10 is substantially reduced, so that the gasket is forced into sealing contact not only with the head 6 and washer 11, but radially with the interior sidewalls of the cup 1 and the exterior walls of the stem 7, thus forming a strong waterproof seal.

In the embodiment shown in Figure 3, the structure is identical with that of Figures 1 and 2, and the mode of assembly is the same, save that in lieu of the supporting cup 4 for positioning the head 6 of the plug, a circumferential crimp 14 is provided about the midsections of the cup 1 and the head 6 of the plug is seated thereagainst, so that the plug is positioned against movements away from the mouth of the case.

From the foregoing description it should be apparent that the invention accomplishes its objects, and provides a closure for electric blasting caps which may be assembled with facility and Without the possibility of distorting or otherwise damaging the ignition assembly. The compression of gasket l0 in situ not only effects a waterproofing of the closure, but also stabilizes and rigidies the interrelation of plug 6 (which .supports the ignition assembly) and case l.

While one complete embodiment of the invention has been `described in detail and certain alternatives indicated, it is to be understood that such disclosure is merely illustrative and not limitative. It is realized that many modications and variations of the embodiments disclosed will present themselves to those skilled in the art without departing from the spirit of the invention, and it is therefore contemplated that such modifications be considered within the purview of the appended claims.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

l. In an electric blasting cap having a case, an eX- plosive charge in the case, and conductors extending through a closure for the case, the improvement which comprises, la plug of relatively rigid molded material having a stem portion of substantially lesser outside dimension than the inside dimension of the case and having a body-portion extending radially outward of the stern portion at one end of the latter,` said body portion having a free t within the case, said plug having been molded about saidconductors and saidplug'. being disposed within said case with the body por-tion thereoat a substantial distance,` from the; mouth of said case and the. stem por? tion projeotingvoutwardly therefrom, a. relativelysot re` silient rubber-like gasket above said bodyV portion and between said stern portion and the. oase, a hard washer fitted` over saidV stern within said case and positioned to maintain said gasket under eompressmn between said washer and said body portion and between Said stem and the interior of said case to seal the same, said ease being `intnrneci to anchor said washer in said position.

2. In the manufaoturo of electrie blasting eaps where. in a case having an open ond is charged with explosive and the open end is closed by a plug through which oon7 doctors extend, the improvement which comprises, mold-l ing the plug about the conductors in a shape providing a body portion of diameter suoh as to have a free tit within the case and an integral stem of substantially smaller diameter. providing an armular gasket of relatively soft resilient rubber-like material, said gasket having a central opening of size suc-:h as to be received over said sternaridhaving `an exterior dimension such as to be freely received within said case, insert-ing the plug and gasket within the case With the gasket about said stem and the stem projecting from the body portion toward the open end of said case, applying a Washer to the projecting end of the stern,i thon, after said parts are so Positioned, moving the washer axiallyIl relative to the stem to compress said gasket into sealing relationship between the interior of the oase and, the exterior of the Stem, andl Securing the gasket in such compressed relationship.

Reforenees Cited in the tile of this patent UNITED STATES PATENTS Number Name Date 1,590,364 Grant June 29, 1926 2,144,959 Blackburn- Ian. 24, 1939 ,2,356,337 Miller Aug- 22, 1944 2,428,884 Lefren Oct. 14, 19147 2,429,490 Seherrer Qct. 21,' 1947 2,521,858 Smart Oct. 31, 1950 

